A port is a communication endpoint. At the software level, within an operating system, a port is a logical construct that identifies a specific process or a type of network service.
A port number is always associated with an IP address of a host and the protocol type of the communication.
The lowest numbered 1024 port numbers identify the historically most commonly used services, and are called the well-known port numbers. Higher-numbered ports are available for general use by applications and are known as ephemeral ports.
A port number is a 16-bit unsigned integer, thus ranging from 0 to 65535.
| Port Number | Assignment |
|---|---|
| 20 | FTP Data Transfer |
| 21 | FTP Command Control |
| 22 | SSH |
| 23 | Telnet |
| 25 | SMTP |
| 53 | DNS |
| 67, 68 | DHCP |
| 80 | HTTP |
| 123 | NTP |
| 143 | IMAP |
| 443 | HTTPS |